MicroStation DGN files are supported by the GDB library for read access and limited write access. Both Raster and Vector data may be read from DGN files.
Three formats of Raster Imagery are supported: Compressed Binary, Binary, and Byte. The georeferencing system for raster imagery is PIXEL.
The supported vector entities are LINEs (3), LINESTRINGs (4), SHAPEs (6), ELLIPSE (15 - 2D only), ARC (16 - 2D only), TEXT (17) and TEXT (37). CURVEs (11) are defined by interpolating through all points. SPLINE POLEs (21) are supported as similarly splined polylines.
For CELLs and COMPLEX elements, the individual elements comprising the complex element are read as parts of one shape. Cell components become Rings in GDB.
The georeferencing system for the vectors is PIXEL. Color, line style, line width and text size information is used when creating the direct RST for the layer. White is mapped to black since PCI software uses a white background.
Files with a master unit of DG and sub-units of MN are latitude/longitude files in GDB. Otherwise the georeferencing is just meters. Attribute linkage information becomes additional fields in the GDB layer.
Unsupported entities are ignored during the read operation.
There is limited write access for DGN. Only TEXT, LINE and LINESTRING elements are created. This means that if a DGN file is imported, edited, and exported, the entity types are not preserved.
There are four options that can be used when creating a new DGN file. They are:
/XOff=xxxx an offset in UORS to add to the x value /YOff=yyyy an offset in UORS to add to the y value /SubPerMaster=sss number of sub-units per master units ie meters per kilometer /UORPerSub=uuu number of uors per sub-unit ie millimeters per meter
The XOff and YOff set the Global Origin in the DGN file. The values must be set in UORs. It is suggested that the user select the Global Origin within the the extents of the layer to ensure that the UOR coordinate values do not overflow.
The number of significant digits in the coordinates in the design file is determined by the UORs per Master Unit. For example: For a UTM coordinate with 6 decimal places, use /SubPerMaster=1000 and /UORPerSub=1000. 12 digits need to be used in the XOff and 13 digits in the YOff. The XOff and YOff are typically negative.
The names of the Working Units cannot be set in the Translate window. By default the units are Km and M. The important aspect is to correctly set the SubPerMaster and the UORPerSub values. In MicroStation the unit abbreviation can be changed without affecting the Working Units or coordinate values.
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